The invention relates to contact lenses. In particular, the invention provides contact lenses in which the wearer""s corneal shape is taken into consideration in providing for stabilization and orientation of the lens on the eye.
It is known that correction of certain optical defects can be accomplished by imparting non-spherical corrective characteristics to one or more surfaces of a contact lens, such as cylindrical, bifocal, or multifocal characteristics. The use of contact lenses with these characteristics is problematic in that the lens must be maintained at a specific orientation while on the eye to be effective. However, the lens will rotate on the eye due to blinking as well as eyelid and tear fluid movement.
Lenses designed to maintain their on-eye orientation typically are of two general types. One type uses prism stabilization to maintain the lens orientation. Examples of prism stabilization methods include decentering of the lens"" front surface relative to the back surface, prismatic balancing, thickening of the lower lens edge, supporting the lens on the lower eyelid, forming depressions or elevations on the lens"" surface, and truncating the lens edge.
A second type, dynamically stabilized lenses, uses the movement of the eyelids to maintain lens orientation. Dynamic stabilization methods include reducing the thickness of the lens"" outer surface at two symmetrically lying regions, thickening two outer regions in the horizontal center axis, and thinning, or slabbing off, top and bottom zones on the lens.
The known methods for maintaining lens orientation suffer from a number of disadvantages including that the lenses incorporating the methods require specialized tooling for production, that the lenses are uncomfortable to wear, and that the known methods are not highly effective. Thus, a need exists for a method of maintaining angular orientation that overcomes some or all of these disadvantages.